The invention relates to a method for operating a direct-injection auto-ignition internal combustion engine having a combustion chamber delimited by the cylinder, the cylinder head and the piston of the engine, the piston having a special recess toward which fuel is injected into the combustion chamber, and to an internal combustion engine operated by the method according to the invention.
DE 196 49 052 A1 discloses a diesel engine with direct fuel injection and with a piston recess. The direct-injection auto-ignition internal combustion engine shown there comprises at least one cylinder, a reciprocating piston disposed in the cylinder, a cylinder head and a combustion space delimited by the cylinder, the piston and the cylinder head. Integrally formed into the piston top is a piston recess which in the transitional region to the piston top merges into an essentially annular stepped space. A fuel injector is arranged in the cylinder head for injecting fuel into the combustion chamber. By means of the injector, a plurality of injection jets of fuel are injected, distributed over its circumference, into the combustion chamber along conically arranged jet axes.
The injection jet impinges onto the marginal region of the piston recess. As a result of this, the fuel jet is deflected essentially in two directions. A first part quantity passes downward into the combustion space recess with respect to the axial direction of the cylinder. A second part quantity is directed essentially radially over the piston head toward the cylinder wall. By means of the two part quantities, two combustion fronts, are formed. The second part quantity of fuel directed toward the cylinder wall is not optimal particularly with regard to the formation of soot and nitrogen oxide. The formation of an increased accumulation of soot in the engine oil has been observed.
It is the principal object of the present invention to provide a method for operating a direct-injection auto-ignition internal combustion engine with a reduced generation of soot and smoke. It is furthermore, an object of the present invention to provide a direct-injection auto-ignition internal combustion engine which is suitable for being operated by the method according to the invention.